Not without jumping through some hoops. The OS out of the box won't do that. I don't think you can paste in an icon of a different size either. There are third party applications that let you customize icons. Maybe one of those can do it. Google "customize Macintosh icons".
If the purpose is to make a particular icon "stand out" why not use a color label? Granted, that will only change the "title bubble" color, but if you only have one in the window, it will stand out.
Shop for your Apple, Mac, iPhone and other computer products on Amazon.
We are a participant in the Amazon Services LLC Associates Program, an affiliate program designed to provide a means for us to earn fees by linking to Amazon and affiliated sites.